Testing for the presence of controlled substances has been widely used in government and industry for more than fifteen years. The traditional testing method involves collection of a urine sample from a donor, then sending the sample to a central laboratory for testing. A qualitative screening test is performed on the sample and the results of all of the tested samples are reported to the client, although negative results are often reported earlier than positive or inconclusive results. If a test is positive, it is repeated and the results are evaluated by a neutral third party. The target turn-around time for reporting negative results is 24 hours. There are many factors, however, such as sample transport time, lab staffing and daily volume fluctuations that can delay results. Approximately 85–90% of the samples tested for drugs screen negative. There is an industry need to obtain results from negative drug screens more quickly.
In response to this industry need, manufacturers have developed drug screening tests that can be evaluated at the collection sites. Many on-site test kits are designed to work on urine samples. The kit consists of one or more test strips packaged in a plastic housing. Typically, a technician applies a small amount of a urine sample (e.g. three drops) to a predetermined area on the test kit. The urine is then conveyed through the test strip, for example, by capillary action. Certain areas on the test strip are reactive when brought in contact with a specific drug analyte (e.g., Cocaine, THC, PCP). This reaction causes a change in the appearance of the test strip in that local area. The test strips also include a control area which indicates that the urine has been conveyed to all of the test areas and, thus, provides an indication of when the results of the test may be read. After this area indicates a completed test, the technician reads the test strip and reports the result.
With on-site testing, negative drug screens can be reported to the client in a shorter time period than for laboratory tests. There is a growing interest in the use of on-site testing in the retail industry for pre-employment screening. While these test kits have gained widespread use, they are not without problems. First, the indicator for the drug analyte relies on a chemical reaction which may produce a continuum of results depending on the batch from which the test strip was selected, the age of the test strip and what the person being tested ate or drank before being tested. These variations in the indicators may result in one technician reading a result as a negative while another tester would read the same result as being inconclusive. Because all inconclusive tests must be followed up with a laboratory test and that test evaluated by an independent third party, it would be beneficial if a test could be devised which did not rely on human judgement or on the training or experience of the technician administering the test.
Finally, many test kits require the technician to measure a predetermined amount of urine and apply it to the test kit. This may undesirably bring the technician into contact with the urine.